7GG 


ON     THE 


FLAT-CLAWED    CARNIVORA 


OF    THB 


EOCENE  OF  WYOMING. 


(Read  before  the  American  Philosophical  Society,  April  4,  1873. 


ON  THE  FLAT-CLAWED  CARNIVORA  OF  THE  EOCENE  OF 

WYOMING. 

BY  EDWARD  D.  COPK,  A.  M. 
(Read  before  the  American  Philosophical  Society,  April  4,  1873.) 

MESONYX.     Cope. 

This  genus  was  described  by  the  writer  in  the  Proceedings  of  the 
American  Philosophical  Society  for  1872,  p.  460,  and  published  in  an 
advance  edition  of  the  same  paper  on  July  29th,  1872.  It  was  there  re- 
ferred to  the  Carnivore,  and  stated  to  resemble  Hyanodon  in  some  re- 
spects. I  propose  on  the  present  occasion  to  attempt  a  more  exact 
determination  of  its  structure  and  relationships.  The  only  species  yet 
certainly  referable  to  it  is  Mewnyx  obtusidens,  Cope,  1.  c.,  which  is  repre- 
sented by  a  fragmentary  skeleton.  There  are  preserved,  portions  of  the 
skull  with  the  teeth,  chiefly  mandibular ;  numerous  vertebrae  from  all 
parts  of  the  column ;  parts  of  scapula,  ulna  and  fore  feet ;  portions  of 
pelvis,  femora,  tibiae,  tarsals,  metatarsals.  and  phalanges. 

The  numerous  unguiculate  digits,  the  sectorial  character  of  the  molar 
teeth  and  the  characteristic  form  of  the  astragalus  demonstrate  this 
genus  to  belong  to  the  Garnivora  fissipedia.  It  becomes  interesting 
then  to  determine  the  relations  of  an  Eocene  type  of  the  order  to  the 
families  now  living. 

The  cervical  vertebrce  are  damaged.  The  dorsals  are  strikingly  smaller 
than  the  lumbars,  being  less  than  half  their  bulk.  They  are  opistho- 
coelian  with  shallow  cups,  and  the  centra  are  quite  concave  laterally 
and  inferiorly.  The  centra  of  the  lumbars  are  more  truncate,  with  a 
trace  of  the  opisthoccelian  structure,  and  are  quite  depressed  in  form. 
The  median  part  of  the  series  is  more  elongate  than  in  the  correspond- 
ing vertebra3  of  the  genus  Canis.  They  exhibit  an  obtuse  median  longi- 
tudinal angle,  on  each  side  of  which,  at  a  little  distance,  a  nutritious 
artery  entered  by  a  foramen.  The  zygapophyses  of  the  posterior  lumbars 
have  interlocking  articulations,  the  posterior  with  a  convex  exterior 
articular  face,  the  anterior  with  a  concave  anterior  one.  The  sacrum 
is  not  completely  preserved,  three  coossified  centra  remain.  These  are 
more  elongate  and  the  diapophyses  have  less  expansion  than  in  Felix. 
Rywna,  Cams  or  JTrsus.  They  are  much  flattened,  and  the  middle  one 
has  two  slight »  median  longitudinal  angles.  The  caudal  vertebrae  in- 
dicate a  long  tail,  with  stout  base.  Its  proximal  vertebrae  are  depressed, 
and  with  broad  anteriorly-directed  diapophyses.  The  more  distal  verte- 
brae have  sub-cylindric  centra ;  the  terminal  ones  are  very  small. 

The  glenoid  cavity  of  the  scapula  is  shallow ;  the  coracoid  process  is  a 
short  hook  separated  by  a  strong  groove  from  the  edge  of  the  former. 
The  spine  is  well  developed.  In  the  character  of  the  coracoid,  this 
genus  resembles  Felis  more,  than  Ganis  or  Ursus.  The  ulna  exhibits 
little  trace  of  articular  face  for  the  radius,  less  than  in  Felis  or  Ganis. 


Its  humeral  glenoid  face  is  more  convex  transversely  in  its  anterior  or 
vertical  portion  than  in  those  genera,  and  a  little  more  than  in  Ursus. 
In  the  hind  limb  the  femur  resembles  that  of  other  Carnivora  in  all 
essentials.  The  rotular  groove  is  narrow  and  elevated,  the  inner  margin 
a  little  higher.  The  condyles  are  rather  narrow,  the  inner  with  less 
transverse  and  antero-posterior  extent,  and  separated  by  a  wide  and 
deep  fossa.  The  patella  is  narrow,  thick,  and  truncate  at  one  end.  The 
proximal  end  of  the  tibia  exhibits  a  very  prominent  and  well  elevated 
crest  or  spine,  which  bounds  a  deeply  excavated  fossa.  The  articu- 
lar faces  are  separated  by  a  deep  notch  behind ;  the  external  is  a 
little  the  larger  and  is  produced  into  a  point  outwards  and  backwards  ; 
it  lacks  the  notch  of  the  antero-exterior  margin  so  distinct  in  Canis,  but 
possesses  an  emargination  at  the  outer  base  of  the  crest  homologous 
with  it.  The  general  form  is,  however,  more  like  that  of  Canis  than  of 
Fells,  and  least  like  that  of  Ursus.  The  distal  extremity  of  the  tibia 
presents  Carnivorous  characters.  The  two  trochlear  fossae  are  deeply 
impressed,  the  outer  wall  of  the  external  one  being  formed  by  the  fibula 
only.  The  anterior  marginal  crest  is  more  elevated  than  the  posterior, 
and  presents  an  overlapping  articular  face  between  the  fossa)  for  a  cor- 
responding tuberosity  of  the  neck  of  the  astragalus.  The  inner  malleolus 
is  entirely  without  the  groove  for  the  tendon  of  the  tibialis  posticus 
muscle,  and  therefore  different  from  many  of  the  digitigrade  Carnivora. 
It  has  an  ovate  truncate  surface.  On  the  anterior  face  opposite  the 
inner  trochlear  groove  is  a  rather  small  but  deep  fossa. 

The  astragalus  has  an  elongate  oblique  neck  and  a  navicular  extremity 
slightly  expanded  inwards.  The  trochlear  ridges  are  well  elevated,  and 
not  very  oblique  to  the  true  vertical  plane,  being  much  as  in  the  dog. 
The  distal  extremity  is  quite  different  from  Felis,  Hycena,  Canis  and 
Ursus  in  having  a  rather  narrow  convex  facet  next  the  cuboid  bone  ex- 
tending from  front  to  rear,  and  in  having  the  navicular  facet  pulley-like 
or  slightly  concave  in  transverse  section,  while  it  is  strongly  convex 
antero-posteriorly.  This  is  part  of  the  peculiarity  presented  by  the 
hind  foot  in  this  genus.  Behind  the  navicular  facet,  on  the  superior 
face,  is  a  tuberosity  which  stops  the  flexure  of  the  foot  by  contact  with 
the  tibia  ;  a  trace  of  it  is  seen  in  the  dog.  The  calcaneum  has  the  com- 
pressed form  of  the  digitigrades,  but  the  broader  interval,  and  convex 
external  astragaline  facets  resemble  much  more  those  in  the  bears.  The 
cuboid  facet  is  a  frustrum  of  a  triangle  with  the  apex  directed  inwards 
and  downwards. 

The  metapodial  bones  are  rather  elongate,  and  flattened  so  as  to  be 
transverse  in  position.  A  second  metatarsal  is  more  flattened  than 
corresponding  bones  of  Canis  and  Felis.  Its  cuneiform  facet  is  some- 
what concave  transversely.  The  phalangeal  condyles  are  furnished  with 
an  anterior  and  inferior  carina,  which  is  wanting  above  ;  the  articular 
face  is  wide  above  as  in  Canis,  and  is  bounded  by  a  transverse  fossa  as 
in  digitigrade  genera.  The  phalanges  of  the  first  series  are  elongate 


3 

and  curved  as  in  Felts,  being  relatively  longer  than  in  Ursus.  Phalanges 
of  the  other  series  are  quite  short.  The  ungues  are  short  and  flattened, 
their  inferior  surface  is  nearly  plane,  and  the  superior  but  little  convex. 
A  shallow  groove  divides  the  upper  face  longitudinally  to  the  ex- 
tremity. The  margin  below  is  acute  to  a  slightly  contracted  neck. 
There  is  no  indication  of  collar  for  reception  of  the  horny  sheath,  except 
perhaps  a  slight  area  of  fracture  on  each  side,  and  there  is  no  projecting 
tuberosity  below  for  insertion  of  flexor  tendon.  The  middle  of  the 
proximal  part  of  the  unguis  is  a  raised  plane,  and  on  each  side  of  it,  at 
the  neck,  two  arterial  foramina  enter.  There  is  a  small  foramen  in  the 
groove,  and  several  smaller  ones  near  the  margin.  These  ungues  re- 
semble somewhat  those  of  some  tortoises.  They  were  found  with  the 
other  phalanges,  with  which  they  agree  in  size  and  articulation,  and  no 
doubt  belong  to  the  same  animal.  It  is  evident  that  they  differ  in 
character  from  those  of  most  existing  Carnivora.  The  penultimate 
phalanges  agree  with  them  in  the  depressed  form  of  their  proximal  ar- 
ticular faces,  wanting  entirely  the  triangular  form  so  characteristic  of 
Carnivora,  especially  of  the  cats  and  dogs.  The  short  flat  shaft  of  the 
same  is  almost  equally  peculiar. 

The  cranium  is  fragmentary.  The  malar  bone  of  the  right  side  is 
similar  in  position  and  form  to  that  of  the  C unities,  especially  in  the 
presence  of  a  weak  angle  only,  to  mark  the  posterior  border  of  the  orbit. 
It  has*  a  much  less  expanded  union  with  the  maxillary  than  in  these 
animals,  and  is  proximally  shallower,  thicker  and  more  prominant.  Its 
posterior  portion  is  more  plate-like. 

There  are  numerous  teeth  preserved,  but  separate  from  the  skull  and 
mostly  mandibular.  The  inferior  canine  is  stout  especially  in  the  root, 
which  is  a  flat  oval  in  section.  The  crown  is  but  little  curved,  slightly 
compressed,  and  without  edge  or  groove.  The  premolars  graduate  into 
the  molars,  so  that  the  line  of  distinction  is  not  easily  drawn.  The 
first  premolar  has  a  single  root ;  the  crown  is  slightly  conic,  with  a 
small  tubercle  at  the  base  behind.  This  tubercle  increases  in  size  011  the 
premolars  2  and  3,  and  becomes  on  the  true  molars  a  longitudinal 
cutting  edge  extending  along  the  axis  of  the  crown,  not  much  elevated 
above  a  wide  base.  It  occupies  half  the  length  of  the  crown  in  the 
larger  molars,  and  is  preceded  by  an  elevated  conic  cusp.  In  front  of 
the  base  of  this,  a  small  conic  tubercle  projects  forwards,  which  appeared 
as  a  rudiment  on  the  third  premolar.  The  number  of  mandibular  teeth 
would  appear  to  be,  P.M.  3,  M.  4.  No  portions  certainly  referable  to 
the  superior  molars  were  found. 

Conclusion.  In  summing  up,  it  may  be  accepted  as  a  result  of  the 
above  analysis  that  the  genus  Mesonyx  represents  a  family  of  Carnivorci 
digitigrada,  distinct  from  any  now  living  on  the  globe.  The  form  of  the 
astragalus  renders  it  probable  that  the  inner  toe  is  wanting  or  rudimental, 
and  that  there  were  four  digits  on  the  hind  foot.  The  foot  was  also  short 


4 

and  the  claws  flat, -and  altogether  without  prehensile  use,  but  rather 
adapted  for  aquatic  life.  The  number  of  molars  exceeds  that  in  any  re- 
cent family  of  Carnivora  except  the  Protelidat-,  and  their  sectorial  form  al- 
lies it  at  once  to  the  extinct  Hycenodontida.  To  this  family  the  genus 
Mesonyx  may  indeed  be  for  the  present  referred.  Among  recent  families 
it  approaches  nearest  the  Canidw,  but  has  structures  borrowed  from 
others,  while  its  numerous  molars  constitute  a  point  of  greater  general- 
ization than  any.  Although  sectorials,  this  character  is  not  nearly  so 
marked  as  in  the  existing  Carnivora,  the  cutting  edge  being  obtuse  and 
occupying  half  the  crown  only,  while  the  elevated  cone  occupying  the 
remainder  distinguishes  the  genus  from  these  and  from  Hycenodon  also. 
The  lobe  corresponding  to  this  cone  is  preceded  in  Hycsnodon  by  a 
cutting  edge,  in  Mesonyx  by  a  tubercle. 

MESONYX  OBTUSIDENS.     Cope. 

Proceedings  American  Philosophical  Soc.  1872,  460  (July  29th). 

This  species  was  as  large  as  our  largest  wolves.  While  the  proportions 
of  the  limbs  were  not  very  different,  the  form  was  rather  more  slender 
behind.  The  orbit  was  smaller,  and  the  cheek  bone  more  prominent 
than  in  those  animals.  The  long  tail  added  to  the  general  resemblance 
to  the  dogs.  The  measurements  are  as  follows  : 

M.   ' 

Length  malar  bone 0.073 

Depth  "        in  front 016 

"'  "         at  postorbital  angle 023 

44  •'  middle  of  orbit 015 

Thickness       "  "  "     013 

Transverse  diameter  glenoid  cavity  of  scapula. .-. 025 

"  ••         ulnar       do.      for  humerus 014 

Length  centrum  dorsal  vertebra 019 

Diameter     "        transverse 018 

vertical : .014 

Length  centrum  of  a  median  lumbar 030 

Diameter     ' '        transverse 025 

vertical 016 

••  "        first  sacral 014 

**•  "        transverse       "         026 

Expanse  of  do 046 

Length  of  two  sacral  vertebrae 049 

"         proximal  caudal 022 

Expanse  diapophyses     "     036 

Diameter  centrum  do.,  vertical 009 

"  "  transverse 015 

"  "       distal  caudal,  vertical 007 

"  ««       do.,  transverse 007 


M. 

Chord  of  femoral  trochlea  and  condyles 038 

Width  trochlear  groove 013 

"       condyles *029 

• '       tibia  proximally 038 

Diameter  do.  antero-posteriorly 039 

shaft,  .050  M.  from  end 017 

distal  extremity  transversely 026 

antero-posteriorly 018 

Length  patella 025 

Width         " 015 

Length  astragalus • 030 

Width        "  above 016 

"  distally 017 

"  "  neck 012 

"       cuboid  facet  of  calcaneum 016 

Depth         "        "  "        Oil 

Widtji  of  a  second  metacarpal  (shaft) 012 

Depth  "  "  (head) 014 

Width  "  distal  end 010 

Length  proximal  phalange • 0290 

Width  proximally 0100 

.  "  of  a  penultimate  do 0085 

Length  "  "  .0110 

Length  ungueal  phalange _.0150 

Width  medially 0065 

"       proximally 0070 

Length  crown  of  canine  tooth  (worn) 0200 

Diameter  of  base  fore  and  aft y .     .013 

"          premolar  (1)    "         , 006 

Length  crown  do '006 

"        base  premolar  (2) Oil 

Height  crown        4<  009 

Length  crown  true  molar 018 

Width        "  "          008 

Height  of  cutting  edge 005 

There  are  no  cingula  on  the  teeth,  and  the  enamel  is  perfectly  smooth. 
The  appearance  of  the  crowns  as  well  as  the  bones  indicates  an  adult 
animal. 

The  bones  of  this  animal  were  found  together  on  the  bluft's  of  Cotton- 
wood  Creek,  Wyoming,  by  myself  while  attached  to  Hayden's  Geological 
Survey  of  the  Territories  for  1872. 

SYNOPLOTHERIUM.     Cope. 

Proceedings  American  Philosophical  Society,  1872,  488  (published 
August  20th). 

Represented  as  yet  by  a  single  species,  which  is  known  from  frag- 


6 

mentary  remains  of  a  single  individual.  The  portions  preserved  are  : 
a  large  part  of  the  skull  with  nearly  complete  dentition,  the  superior 
molars  loose ;  lumbar  and  caudal  vertebrae  ;  large  portions  of  both  fore 
limbs,  including  the  bones  of  the  feet;  smaller  portions  of  the  hind 
limbs  and  feet. 

The  bones  of  the  fore  limbs  are  stout  in  their  proportions.  The 
Tiumerm  has  a  well  marked  rugose  line  for  muscular  insertion  on  its 
posterior  face,  but  no  prominent  angle.  Distally  the  inner  and  outer 
condylar  tuberosities  are  almost  wanting,  and  there  is  neither  external 
aliform  ridge,  nor  internal  arterial  foramen.  The  olecranar  and  coronoid 
fosste  are  confluent,  forming  a  very  large  supraeondylar  foramen.  The 
condyles  are  moderately  constricted  medially,  and  there  is  a  well  marked 
submedian  rib  separated  fnom  the  outer  condyle  by  a  constriction.  The 
latter  is  continued  as  an  acute  ridge  on  the  outer  side  of  the  olecranar 
fossa.  The  inner  condyle  is  the  more  prominent  and  its  outer  margin  is 
a  sharp  elevated  crest.  The  ulna  has  a  very  prominent  superior  process, 
continuing  the  cotylus  upwards.  The  coronoid  process,  on  the  other 
hand,  is  rather  low.  The  radial  cotylus  is  flat  and  broad.  The  distal 
end  is  not  preserved.  The  radius  has  a  more  transverse  head  than  Canis 
or  Felis,  and  has  three  articular  planes,  the  inner  being  a  wide  oblique 
truncation  of  the  edge.  The  shaft  is  angulate  below,  and  becomes  a 
little  deeper  than  wide  near  the  distal  end.  The  extremity  is  lost.  The 
carpal  bones  are  probably  all  present.  The  fore  foot  was  found  in  place 
so  that  the  relations  of  the  bones  are  known  with  certainty.  The 
scaphoid  and  lunar  appear  to  be  distinct.  The  former  exhibits  proximal- 
ly  the  inner  tuberosity,  then  a  slight  concavity,  and  then  the  convexity, 
where  it  is  obliquely  truncated  so  as  to  give  a  general  rhomboid  outline. 
Beneath  there  are  but  two  facets,  the  inner  the  deepest,  and  divided 
lengthwise  by  the  truncation  of  the  bone.  The  larger  facet  fits  correctly 
the  0.0.  trapezium  and  trapezoides.  The  lunar  was  not  found  in  its 
place,  but  two  fragments  taken  from  the  matrix  just  behind  it,  adhering 
to  the  pisiforme,  probably  belong  to  it.  The  upper  face  is  convex. 
The  cuneiform  is  large  and  concave  lengthwise  above  for  the  narrow 
extremity  of  the  ulna.  Below  it  has  a  large  concave  facet  for  the 
unciform.  The  pisiforme  is  of  unusual  size,  and  is  as  stout  as  the  largest 
metacarpus,  and  nearly  half  as  long  as  the  outer  (5th)  metacarpal.  It 
articulates  with  a  thick  V-shaped  facet  of  the  cuneiform.  Its  extremity 
is  obtuse  and  expanded.  The  trapezium  is  large  and  attached  to  its 
metacarpus  laterally,  sending  a  process  downwards  posteriorly.  It  sup- 
ports a  narrow  articular  surface  for  the  metacarpus  of  a  small  pollex  or 
inner  digit,  which  is  not  preserved.  The  trapezoid  is  smaller  and  of  a 
triangular  outline,  with  the  base  forwards.  The  magnum  is  a  rather 
small  bone  articulating  as  usual  with  the  metatarsals  2  and  3.  It  is 
depressed  in  front.  The  unciform  is  a  large  bone  with  a  considerable 
external  anterior  surface.  Two-thirds  of  its  upper  surface  is  in  contact 
with  the  cuneiform,  the  remaining  part  projecting  upwards  with  convex 
face  to  unite  with  the  lunare.  Below  it  supports  metatarsals  4  and  5. 


There  were  probably  five  digits  of  the  fore  foot,  the  inner  small  or 
rudimental.  The  proportions  are  stouter  than  in  the  dogs,  but  not  so 
much  so  as  in  the  bears.  The  phalanges  have  a  length  similar  to  that  seen 
in  some  bears,  but  the  metatarsals  are  more  elongate.  The  lengths  of 
the  latter  are,  fifth  shortest,  then  2d,  3d  and  4th.  Their  condyles  are 
broad,  with  median  keel  behind,  and  shallow  supracondylar  fossa  in 
front.  The  first  phalanges  are  about  one-third  the  length  of  the  meta- 
carpals ;  the  second  of  digit  No.  2  broad  and  stout  and  half  as  long  as 
the  phalange  of  the  first  row.  An  ungueal  phalange  has  a  singular 
form,  so  that  the,  claw  might  be  supposed  to  have  a  subungulate  charac- 
acter.  It  is  flat,  considerably  broader  than  high  and  with  expanded  and 
obtuse  extremity.  The  articular  extremity  is  depressed  and  transverse 
concave  in  vertical,  convex  in  transverse  section.  The  anterior  three - 
fifths  of  the  superior  middle  line  is  occupied  by  a  deep  gaping  fissure, 
which  separates  the  extremity  into  two  points.  The  inferior  face  is 
entirely  flat,  there  being  no  tendinous  tuberosity.  The  sides  are  grooved, 
and  give  entrance  each  to  a  large  arterial  foramen  proximally.  These 
claws  resemble  those  of  Nesonyx,  and  differ  remarkably  from  those  of 
existing  terrestrial  Carnivora. 

Of  hinder  limb  the  only  characteristic  pieces  remaining  are  the  navicu- 
lar,  cuboid,  and  an  external  cuneiform  bone.  The  cuboid  is  rather 
stout,  with  a  slight  concave  facet  at  one  extremity  and  two  at  the  other, 
one  of  them  smaller  and  sublateral.  The  navicular  is  wide  and  flat,  and 
with  a  strongly  concave  astragaline  facet.  Below,  it  presents  two  deep 
oblique  concave  facets  for  the  cuneiforms,  with  a  small  sublateral  one 
on  the  outer  side.  The  facets  of  the  cuboid  and  astragalus  indicate  four 
well  developed  digits  and  another  perhaps  smaller  one.  Thus  in  this 
genus  they  were  on  both  limbs  probably  5-5,  with  the  inner  small. 

The  cranium  is  fractured  above*  There  remain  the  squamosal  and 
periotic  bones,  occipital  condyles,  malar  and  part  of  maxillary,  both 
premaxillaries  and  the  greater  part  of  both  mandibular  rami.  The 
squamosal  process  of  the  zygoma  is  produced  inferioiiy  far  below  the 
auditory  meatus,  even  further  than  in  the  bears.  Its  proximal  portion 
includes,  on  the  lower  face,  a  strong  groove  at  right  angles  to  the  axis 
of  the  cranium,  with  its  defining  margins  acute  and  prominent.  This 
is  the  transverse  glenoid  cavity  of  the  carnivorous  type.  The  zygoma 
has  a  wide  curvature  indicating  a  powerful  temporal  muscle.  The  pos- 
terior angle  of  the  malar  extends  well  posteriorly.  Its  anterior  portion 
projects,  forming  a  longitudinal  rib;  there  is  no  produced  postorbital 
prqpes's.  The  tympanic  bone  is  produced  upwards  and  outwards  and 
forms  a  tube  with  everted  lips.  The  opisthotic  (mastoid)  separates  it 
entirely  from  the  exoccipital,  and  overlaps  the  posterior  half  of  the  tube 
by  a  laminar  expansion.  A  pit  in  this  bone  near  the  meatus  externus 
represents  the  insertion  of  the  stylohyal  ligament.  There  is  no  bulla, 
the  tympanic  chamber  being  small  and  with  thick  walls.  The  character 


8 

of  tliis  region  forbids  the  idea  of  any  tapiroid  affinities  on  the  part  of 
this  genus,  and  resembles  that  seen  in  the  bears  more  than  that  of  any 
other  carnivorous  type. 

The  premaxillaries  are  vertico-oblique  in  position,  presenting  the 
nareal  opening  directly  forwards  as  in  cats,  but  with  a  still  less  promi- 
nent alveolar  border.  The  horizontal  part  of  this  border  is  indeed  very 
short,  including  but  two  small  incisors.  It  then  rises  vertically,  and 
turns  obliquely  backwards  to  the  maxillary,  enclosing  a  deep  sinus  with 
the  canine  tooth.  From  the  anterior  side  of  this  sinus  the  larger 
external  incisor  issues,  with  its  root  extensively  exposed  externally.  A 
rib  ascends  from  the  front  o  f  its  alveolus  to  the  anterior  or  nareal  margin 
of  the  bone.  The  triturating  surfaces  of  the  incisors  are  directed  back- 
wards, and  the  alveolar  edge  is  thickened  in  front  of  them  with  a 
tuberosity.  The  teeth  are  much  worn  so  that  the  forms  of  the  crowns 
cannot  be  determined,  but  projecting  .25  inch  beyond  the  alveoli  they 
are  compressed,  the  large  outer  tooth  with  a  longitudinal  angle  in  front. 

The  mandibular  rami  are  quite  elongate,  and  indicate  a  cranium  near 
the  size  of  that  of  the  brown  bear  (  Ursus  arctos).  Their  form  is  slender, 
and  they  have  a  long,  rather  narrow,  symphysis,  which  projects  obliquely 
forwards.  The  angle  is  not  preserved.  »The  mental  foramen  is  large 
and  issues  just  behind  the  canine  teeth. 

The  dentition  is  I.  ?j}  ;  C.  1 1  M.  ?|.  The  canine  is  of  very  large  size 
especially  the  part  protruded  beyond  the  alveolus.  The  crown  is  stout 
at  the  base,  but  is  soon  compressed  and  obliquely  truncated  by  the 
attrition  of  the  inferior  canine,  on  its  inner  face.  Two  superior  molars 
preserved  are  three-rooted,  and  the  section  of  the  crown  is1  more  or  less 
equally  trilobate.  The  number  in  the  maxillary  bone  is  estimated  at 
seven,  the  number  found  in  the  ramus  of  the  mandible.  There  are  six 
two-rooted  molars  below  and  probably  one  single-rooted  premolar, 
though  this  is  indicated  by  an  alveolus  only.  The  molars  are  rather 
narrow  antero-posteriorly,  and  are  not  very  different  in  size,  except  that 
the  penultimate  is  a  little  longer,  ?,nd  the  last  a  little  shorter  than  the 
others.  There  was  evidently  a  longitudinal  cutting  edge  behind,  and 
some  other  shorter  process  on  the  front  of  the  crown ;  the  edge  is  pre- 
served on  the  last  tooth  and  resembles  that  of  Mesonyx,  so  that  I  have 
little  doubt  that  the  remainder  of  the  tooth  was,  as  in  that  genus,  a  conic 
tubercle.  The  .most  remarkable  feature  of  the  genus  is  seen  in  the 
inferior  canines.  These  are  very  large  teeth,  and  are  directed  im- 
mediately forwards,  as  in  the  case  of  the  cutting  teeth  of  rodents. 
They  work  with  their  extremities  against  the  retrorse  crowns  of  the  two 
external  incisors  above;  and  laterally  against  the  superior  canine.  They 
are  separated  by  a  space  about  equal  to  the  diameter  of  one  of  them. 
In  this  space  I  find  no  alveoli  nor  roots  of  teeth ;  the  outer  alveolar  wall 
extends  far  beyond  the  inner.  The  latter  terminates  opposite  the  middle 
of  the  superior  canine.  It  may  be  that  there  are  no  inferior  incisors. 


9 

Some  of  the  vertebrae  display  stout  triangular  neural  spines;  on  the 
lumbars  the  posterior  zygapophyses  are  embraced  laterally  by  the 
grooved  correspondents  of  the  succeeding  vertebra.  Some  of  the  caudal 
vertebrae  are  long,  slender  and  without  neural  arch,  indicating  that  this 
genus,  like  Mesonyx,  had  a  long  slender  tail. 

Affinities.  Having  described  the  available  parts  of  this  form,  it  re- 
mains to  consider  its  place  in  the  zoological  system.  The  structure  of 
the  dentition  of  the  upper  jaw,  with  the  mode  of  articulation  of  the 
mandible  remove  it  from  such  orders  as  Eodentia  and  Edentata;  the 
only  remaining  ones  with  which  it  is  necessary  to  compare  it  are  the 
Perissodactyla,  Proboscidia  and  Carnivora.  As  many  of  the  diagnostic 
bones  are  wanting,  it  is  necessary  to  rely  on  collateral  and  empirical 
indications  of  relationship.  From  tapiroid  types  the  development  of 
the  tympanic  region  distinguishes  it.  From  Proboscidians  the  slender 
feet  and  reduced  ulna,  as  well  as  the  longitudinal  crests  of  the  teeth 
separate  it.  It  then  remains  to  compare  it  with  Perissodactyles  of  the 
types  which  possess  strong  canine  teeth.  In  points  of  resemblance  to 
these  we  have  the  flat  claws  and  separate  scaphoid  and  lunar  bones, 
nevertheless  the  greater  number  indicate  truer  affinity  to  the  Carnivora. 
Such  are  the  external  transverse  glenoid  cavity,  the  teeth  with  longi- 
tudinal crests,  the  slender  digits,  the  well  developed  tympanic  bone ; 
confirmatory  are  the  large  canine  teeth,  the  incomplete  orbit,  aiid  the 
projecting  inner  condyle  of  the  humerus.  The  form  of  the  claws  is  not 
absolutely  incompatible  with  the  same  order,  as  it  is  approximated  by 
some  of  the  Seals. 

Among  Carnivora,  the  feet  are  like  both  dogs  and  bears.  The  very 
prominent  postglenoid  ridge,  and  the  narrow  tympanic  chamber*  are 
decided  points  of  resemblance  to  the  bears,  but  the  cavu'm  tympani  is 
even  less  expanded  than  in  those  animals.  The  characters  of  dentition 
are  more  like  those  of  the  Hycenodontidce  and  Mesonyx  than  any  other 
group,  and  even  the  remarkable  incisor-like  inferior  canines  are  ap- 
proximated by  the  anteriorly  directed  canines  of  Hytxnodon  leptorliynchus, 
Laiz.  et  Par. 

As  a  summary,  it  may  then  be  concluded  that  the  j;enus  SynoflotJterium 
is  a  Carnivore,  presenting  a  number  of  points  of  resemblance  to  the 
bears,  and  to  the  extinct  Hywnodons;  but  that  its  distinct  scaphoid 
and  lunar  bones,  and  flat  claws  ally  it  to  other  fofms  of  Mammalia,  show- 
ing it  to  be  a  more  generalized  type  of  the  order  than  either  of 
the  above.  The  peculiar  approach  of  the  lower  canines  is  a  special 
modification  for  peculiar  habits,  which  I  suspect  to  have  been  the 
devouring  of  the  turtles  which  so  abounded  on  land  and  in  the  waters 
of  the  same  period.  The  slender  symphysis  could  most  'readily  be  in- 
troduced into  the  shell,  while  the  lateral  pressure  of  the  upper 
canines  with  the  lower,  would  be  well  adapted  for  breaking  the  bony 
covering  of  those  reptiles.f  It  is  not  unlikely  that  this  genus,  Mcwny.r, 

*  See  Prof.  Flower's  Osteology  of  Mammalia  on  this  point. 
t  See  Proceed.  Amer.  Plulos.  Soc.  1872,  p.  484. 


10 

and  possibly  Hyaznodon  form  part  of  the  lost  series  which  terminated  in 
the  Seals  of  the  present. 

SYNOPLOTHEBJTJM  LANIUS.     Cope. 
Proceed.  Ame,r.  Phitos.  Soc.,  1872,  p.  483. 

The   cranium  of  this   species  is  rather  less  than  that  of  the  grizzly 
bear,  while  the  other  bones  do  not  indicate  so  large  an  animal. 

Measurements. 

M. 

Length  glenoid  cavity 0.045 

Width        "  "      025 

Diameter  zygomatic  fossa *  .058 

Width  opisthotic  inside  for.  stylohyoideum 014 

Diameter  meatus  auditorius  externus 012 

cavum  tympani 009 

Length  ramus  mandibuli  preserved 228 

"      of  series  of  seven  molar  teeth 131 

lf          last  molar,  crown 0155 

Width  "  "      0080 

Length  of  penultimate    "      0215 

Width  "  "      0100 

Length  exposed  part  of  inferior  canine 024 

"  "  superior      "      032 

"  "  outer  upper  incisor 023 

Piameter  triturating  surface  inferior  canine 028 

"        do.,  transverse 0166 

"        superior  canine  (antero-posterior) 024 

"        of  the  two  inner  incisors 010 

"        of  exterior  incisor  (oblique) 010 

"        symphysis  mandibuli 044 

"        nareal  orifice 040 

Depth  "  "      031 

"  mandibular  ramus  at  M.  6 049 

Thickness  below  of  do 014 

Length  of  a  superior  molar  crown 020 

Diameter  condyle  of  humerus 047 

"         shaft  "        (compressed) 0410 

"         condyles  "         0415 

"  "  "        (antero-posterior) 032 

"         head  radius  (transverse) 0282 

"          "       (vertical) 0162 

"  »     shaft  radius 016 

"         cotylus  of  ulna  (long) 030 

Depth  ulna  at  coronoid  process 034 

Length  carpus  and  digit  2  without  unguis 112 

"        two  phalanges  do 037 

"        metacarpal  do 061 


11 

Measurements. 

M. 

Length  metacarpal      No.  3 074 

"  "  No.4 070 

"  "  No.  5 053 

"        scaphoid  transversely 023 

"        cuneiform         "  027 

"        pisiform 027 

Width        "         distally 016 

Length  unciform  transversely 020 

Width  "        antero-posteriorly '. 013 

"         trapezoid  "  0155 

"         trapezium  "  0114 

Length          "          vertically 016 

Width  scaphoid  antero-posteriorly 015 

'   "       navicular  "  0155 

Length        "        transversely 0255 

"        ungueal  phalange 016 

Width         "  "          010 

Diameter  centrum  of  lumbar  vertebra 029 

"  "  caudal          "        009       . 

The  dental  series  is  uninterrupted  from  the  canine  if,  as  I  believe, 
there  is  an  alveolus  for  a  simple  premolar  behind  it.  This  I  overlooked 
when  first  describing  the  species  and  hence  gave  the  molars  as  6  instead 
of  7.  The  superior  canine  is  smooth,  but  the  inferior  one  of  the  left 
side  has  a  longitudinal  groove  on  its  extero-inferior  face. 

Restoration.  This  carnivore  had  a  large  head,  with  a  long,  rather  nar- 
row, and  truncate  muzzle.  The  limbs  were  relatively  smaller,  not  ex- 
ceeding those  of  the  black  bear  (  Ursus  americanus),  in  length  and  thick- 
ness. The  tail  was  long  and  slender  as  in  the  cats,  while  the  claws  were 
broad  and  flat  as  in  the  beaver. 

History,  Locality,  etc.  The  teeth  are  very  much  worn,  indicating  the 
hard  food  on  which  the  animal  had  subsisted,  as  well  as  its  mature  age. 

I  originally  described  this  species  as  resembling  the  remarkable  genus 
Anchippodus*  of  Leidy,  and  subsequently  (on  the  Short-footed  Ungu- 
lata  of  Wyoming,  etc.,  p.  5)  have  alluded  to  the  large  rodent  incisor-like 
teeth  as  though  they  were  homologous  in  the  two  genera.  I  there 
identified  those  teeth  in  Synoplotherium  as  canines,  adding  that  they 
were  probably  the  same  in  Anchippodus.  Having  determined  the  car- 
nivorous affinities  of  the  former  genus,  the  homology  of  these  apparently 
similar  teeth  in  the  latter  becomes  problematical.  With  our  present 

*  See  in  Hayden's  Geol.  Surv.    Montana,  1871  (as  Trogosus). 


12 

knowledge,  the  type  of  molar  teeth  in  AncMppodus  resembles  that  of 
many  ungulates,  and  it  is  not  therefore  probably  allied  to  Synoplotherium. 
Nevertheless  it  is  far  from  certain  that  the  teeth  in  question  are  incisors, 
and  that  the  genera  are  in  nowise  related,  though  a  similar  modification 
of  a  remarkable  character  in  distinct  but  co-existent  types  is  by  no 
means  an  unprecedented  circumstance. 

The  remains  on  which  the  above  identification  is  based,  were  found 
by  the  writer  on  a  terrace  of  the  Mammoth  Buttes  near  South  Bitter 
Creek  in  Wyoming.  The  cranium  and  fore  foot  and  leg  were  excavated 
from  the  deposit. 

Formation,  the  Bridger  Group  of  the  Eocene  of  Hayden. 

Prof.  Marsh  has  described  two  genera  of  Carnivora  from  the  same 
formation,  embracing  species  approaching  this  one  in  size.  They  are 
both  distinguished  by  the  broader  forms  of  the  crowns  of  the  inferior 
molar  teeth  and  other  points. 


EXPLANATION  OF  PLATES. 

Plate  I.  Skull  of  SynoplotJierium  lanius,  .6  iiat.  size  ;  tf,  the  tympanic    • 
and  opisthotic  bones  of  the  left  side. 

Plate  II.  Fig.  1,  End  of  muzzle  of  cranium  of  the  same,  from  front  : 
fig.  2,  the  same  from  below.  Fig.  3,  metapodium,  etc.  of  left  fore  foot. 
Fig.  4,  scaphoid  bone  of  the  same  foot,  a  above  ;  5  below.  Fig.  5,  Un- 
gueal  phalange  separate. 


APRIL  19TH,  1873. 


4-a. 


5a. 


5c. 


5b. 


Fig.  7 and 2,  % n<i£.size';   3.4,5, 


